The invention relates to an equipment for the production of images of a test object using nuclear magnetic resonance. Such equipment includes means for applying magnetic primary and gradient fields to the test object and for picking up the deflection of the nuclear spins of the test object from their equilibrium position caused by a radio-frequency magnetic excitation pulse. With a plurality of gradients in a cross-sectional "slice" of the test object, a projection of the nuclear spins on a frequency axis is picked up as a Fourier row and from the Fourier rows an image of the respective examined slice is calculated by Fourier transformation. The equipment also includes means for controlling the acquisition of the Fourier rows as a function of a "motion" signal representing the motion of an organ.
It is known that, in particular the hydrogen nuclear spins of a test object can be deflected away from a preferential direction, generated by a magnetic primary field, by a radio-frequency excitation pulse. After termination of this excitation pulse these spins swing back into the preferential direction only after a certain time. During this time the spins precess with a frequency which depends on the intensity of the magnetic primary field. This precession can be detected with an RF antenna and corresponding receiver circuits. By superimposing a first field gradient on this homogeneous magnetic primary field so that the magnetic field distribution varies spatially, it is possible to locate the spins in one spatial direction--namely, the gradient direction--over the respective measured frequency.
It is also known that, by brief application of a second field gradient of variable amplitude or duration, orthogonal to the first gradient, a location coding in a second spatial axis can be carried out before the signals in the first gradient are read out, thereby to create cross-sectional images of a test object. The excitation in a slice of the test object is brought about by the fact that the magnetic primary field is influenced by an additional third field gradient, normal to the first and second gradients, such that the excitation of the spins takes place only in this slice. This is possible because the excitation occurs only with a frequency which is strictly correlated to the magnetic field in the desired slice. This method is described for example in the German published Patent Application No. OS 2,611,497 (corresponding to U.S. Pat. No. 4,070,611).
Due to the multiplicity of necessary measuring processes, a complete measurement for a cross-sectional slice takes so long that organ movements in the test object, for example movements due to heartbeat or respiration, show up as interferences in the generated image. To avoid such interferences, it is a known practice to control the test value acquisition as a function of the EKG and/or the respective respiration phase of the patient. Under respiration phase control, the acquired measured value is released and utilized only in a relatively short time span of each respiration phase. However, since only a small percentage of the available information is utilized, this technique results in a considerable increase of the measurement time, which is not always acceptable in the practice.